1. Field
The present invention relates to a method and apparatus to reduce dielectric discharge in liquid crystal cells or devices driven with high voltages.
2. Related Art
As shown in FIGS. 1A-1C, the prior art uses a photolithography process to deposit a gold layer 12 on conventional conductor films 44 inside a large conventional liquid crystal cell 58. Generally, conventional liquid crystal cell 58 comprise a pair of substrates 2 facing each other. Each substrate 2 has a conventional conductive film 44 on top of it on a side of the substrate 2 facing the other substrate 2. Conventional conductive films 44 are connected by a drive signal supply 20 (e.g., a voltage signal generator). On top of each conventional conductive film 44 are polymer-dispersed or cholesteric liquid crystals (not shown), which would require high operation voltage. Drive signal supply voltage 20 is an AC signal generator that supplies the necessary high voltage to drive conventional liquid crystal cell 58.
In liquid crystal devices that contain polymer-dispersed or cholesteric liquid crystal materials, high voltages are necessary to overcome the polymer network elasticity or helical twisting power on the molecular level to tune or switch the device for a desired electro-optical effect. In these liquid crystal cells, electric fields higher than 15 V/μm or voltages higher than 100 volts need to be applied.
However, due to the use of high voltages, conventional liquid crystal cells 58 created through the photolithography process are prone to unwanted dielectric discharges. Dielectric discharges usually trigger a dramatic cascading effect and evaporates a certain amount of liquid crystal material inside a liquid crystal cell. Such dielectric discharges can severely damage the liquid crystal cells and render it inoperable.
In FIG. 1A, a photoresist 10 is etched to create a gap 8. Gold 6 is deposited over photoresist 10 and gold 6 is deposited in gap 8 to form gold layer 12.
In FIG. 1B, after gold 6 and photoresist 10 are removed, gold layer 12 remains on top of conductive film 44. However, when photoresist 10 is removed, “dog ears” or gold sharp tips 14 are left on the edge of gold layer 12. This is problematic, because as shown in FIG. 1C, gold sharp tips 14 can cause a dielectric discharge 18 of conventional liquid crystal cell 58.
As shown in FIG. 2, dielectric discharges 18 can also occur when gold sharp tips 14 break off from gold layer 12 creating conductive particles 16 on top of conventional conductive film 44.
Dielectric discharges 18, however, are not limited to liquid crystal cells with gold layer 12 created through the photolithography process. As shown in FIG. 3, a conventional liquid crystal cell 60 comprises conventional conductive films 44 connected by the drive signal supply voltage 20. Each of the conductive films 44 are positioned on top of the substrate 2. One portion of the substrate 2 is enclosed by a peripheral seal 32. In FIG. 3, dielectric discharges 18 can also occur around the sharp edges of ends 50 of the conductive layer 44.
Furthermore, conventional manufacturing processes for photolithography are also inefficient. FIG. 14 demonstrates a conventional process fabricating single-pixel liquid crystal cells for a pop-up filter with a very high contrast ratio. As shown in FIG. 14, the substrate 2 is manually cleaned one-by-one in step S1400. Then, the conventional conductive film 44 is deposited in step S1402 at the rate of 6 liquid crystal cells being completed per batch. In step S1404, the substrate 2 is manually cleaned one-by-one again. In step S1406, the conductive film 44 is patterned through the photolithography process one-by-one. In step 1408, the substrate 2 is again cleaned manually one-by-one. Then, in step S1410, a gold ring such as gold layer 12 is deposited with approximately 24 liquid crystal cells being completed per batch. Then, the substrate 2 is cleaned manually one-by-one in step S1412. Anti-reflective coating is then performed at approximately 36 liquid crystal cells per batch in step S1414. As shown in FIG. 14, the conventional manufacturing process can be inefficient. Furthermore, such a process is also unclean.
Thus, there is a need for a liquid crystal cell which is more resistant to dielectric discharges. There is also a need for a manufacturing process of liquid crystal cells which is more efficient.